Normal reference values for glomerular filtration rate: what do we really know?

Area of Science:

• Nephrology
• Clinical Chemistry

Background:

• Chronic kidney disease (CKD) diagnosis relies on proteinuria and glomerular filtration rate (GFR).
• Defining normal GFR reference values involves differing methodologies.
• Current guidelines use a fixed GFR threshold, potentially overlooking age-related physiological changes.

Purpose of the Study:

• To compare two methods for defining normal GFR reference values: the 'classical way' (measuring healthy individuals) and the 'prognostic way' (fixed cut-off based on mortality risk).
• To evaluate the impact of age on GFR reference values.
• To highlight discrepancies in GFR definitions and propose improvements.

Main Methods:

• Comparison of GFR values obtained through direct measurement in healthy populations versus a fixed threshold.
• Analysis of age-specific GFR decline.
• Critical review of existing GFR cut-off values in CKD guidelines.

Main Results:

• Classical GFR reference values in healthy individuals under 70 years are typically above 60 mL/min/1.73 m2.
• GFR naturally decreases with age; values below 60 mL/min/1.73 m2 may be normal in adults over 70.
• A fixed GFR cut-off of 60 mL/min/1.73 m2, as used in K-DIGO guidelines, inadequately accounts for age.

Conclusions:

• There is a significant discrepancy between age-independent and age-dependent GFR reference values.
• Incorporating age more effectively into GFR definitions is essential for accurate CKD diagnosis and management.
• Revising GFR reference ranges to better reflect age-related physiological changes is recommended.